Variable high resistor



April 17, 1956 W. L. MElER VARIABLE HIGH RESISTOR Filed Nov. 22, 1952 +II I I I I I I I I I CURRENT I 50v. lOOv. l50v.

VOLTAGE v.

WILBER L. MEIER INVENTOR.

ATTORNEY United States Patent VARIABLE HIGH RESISTOR Wilber L. Meier,Chatham, N. J., assignor to Gera Corporation, New York, N. Y., acorporation of New Jersey A Application November 22, 1952, Serial No.321,999

3 Claims. (Cl. 315-337) This invention relates to circuit componentswhich can be adjusted to a desired value of resistance. It hasparticular reference to a gas discharge-device having a relativelyconstant source of ionization, thereby permitting small current valuesto be passed through the device while subjected to a Wide range ofvoltages.

In certain types of electronic circuits it is desirable to employresistance elements which have values of 100 megohms to megohms. This isparticularly true in circuits which are used with photoelectric cellsand detectors of charged particles such as ion chambers. In the pastsuch components have been made of composition material or of a sputteredfilm deposit in a vacuum container. These resistors are costly to makeand are not reliable, changing their resistance values with time andtemperature changes.

The present invention not only is reliable but is also adjustable withina wide range of resistance values and retains this value for longperiods of time. It can be manufactured at a fraction of'the cost ofprior art resistors.

One of the objects of this invention is to provide an improved variableresistor of high resistance value which avoids one or more of thedisadvantages and limitations of prior art arrangements.

Another object of the invention is to reduce the cost of high resistanceunits.

Another object of the invention is to provide a resistance unit which isadjustable within a wide range of values.

Another object of the invention is to simplify and improve theconstruction of resistors having values greater than 100 megohms.

The invention comprises a closed envelope of glass having threeelectrodes within the envelope. One of the electrodes consists'of asheetof conductive material having a small quantity of radioactivematerial on its surface or imbedded in the sheet. A second electrodeconsists of a wire positioned parallel to the sheet. Lead-in conductorsto these two electrodes form the terminals of the resistance unit. Athird electrode consists of a wire positioned parallel to the secondelectrode. This electrode is used as the control means to alter theresistance between the other two electrodes.

For a better understanding of the present invention, together with otherand further objects thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

Fig. 1 is a cross sectional view of the resistor unit.

Fig. 2 is a cross sectional view of the resistor unit taken along line2-2 of Fig. 1.

Fig. 3 is a schematic diagram of connections to illustrate the method ofderiving characteristic curves which illustrate the operation of thedevice.

Fig. 4 is a chart showing a series of curves plotted between ,voltageand current values and indicating the extent of the control circuit.

' in a generally symmetrical arrangement.

Fig. 5 is 'a diagram of connections showing one application of theresistor to a measuring circuit.

Referring now to Figs. 1 and 2, an envelope 10, generallyof glass, isemployed to house the electrodes. A cylindrical electrode 11 having alead-in conductor 12 is mounted within the envelope and contains a smallquantity of radioactive material, such as radium, imbedded in its insidesurface. Radium has been found to be a suitable radioactive materialbecause it gives off alpha particles which cause strong gas ionization.Other radioactive materials may be used instead of radium as long astheir emissions cause sufficient gas ionization to carry the currentbetween electrodes.

' A pair of wires 13 and 14, having lead-in conductors i5 and 16, aremounted in the central part of the envelope One of these electrodes isused in conjunction with the cylindrical electrode to form the theresistor and the other wire electrode is used as a control element. Theenvelope may be filled with an inert gas, such as nitrogen or argon, ata pressure which may be as high as atmospheric pressure or much higher.

Fig. 3 shows a circuit which can be used to determin the characteristicsof the discharge device. T

The circuit uses two sources of potential 17 and 18, each connected to avoltage divider 20, 21 for obtaining desired values of voltage whichcanbe applied to selected electrodes in the resistor element. Ammeters22 and 23 are connected in series with the two wirexelectrode lead-inconductors 15 and 16 to measure the currents. The lead-in conductor 12connected to the cylindrical electrode is connected to a common terminalwhich is also connected to the negative terminals of the batteries.

The results of the circuit shown in Fig. 3 are plotted in a chart, Fig.4. When both Wires are connected together and the voltage varied bychanging the setting of voltage divider 20, the curve A results showinga rapid rise in current at voltages less than 15 volts and showing analmost fiat horizontal characteristic above 15 volts. These values canbe altered by changing the spacing, the pressure, or the amount ofradioactivity in the envelope, the present values applying to a samplemade at atmospheric pressure and having an envelope about 4 inch indiameter and about inch long. The flat portion of the curve is caused bythe constant amount of ionization delivered by the radioactive surface.At 15' volts all of the ions and electrons generated by the alphaparticles are drawn to the electrodes and at higher voltages no more canbe attracted to the electrodes because no more exist in the envelope.

If, now, the voltage of one of the electrodes V2 be set at 50 volts andanother set of current values observed while the applied voltage V1 isvaried, the curve B results. At the point where V2=V1=50 volts thecurrent will divide equally between the two wire electrodes and thecurrent to each electrode has a value just one-half of curve A. AsV isincreased the current to the associated wire electrode 13 increases butnever quite reaches the value of curve A, since the voltage on electrode14 always attracts some electrons and therefore draws a small current.

If the voltage of electrode 14 be kept constant at volts, a similarcurve will result, each Wire electrode carrying half the current whentheir applied voltages are equal (curve C) and tapering off at othervoltage values in a manner similar to that shown in curve B.

Curve D is similar to the other two curves B and C, except that voltageVa is kept constant at volts. It will be obvious, from a study of theabove described curves, that a change of voltage applied to one wireelectrode will alter the resistance value between the other two.Assuming that the current value of the flat part of curve A to be 10-amperes, the value of resistance of point 25 on curve B is approximately10 ohms, the resistance of point 26 on curve C is approximately 2X10ohms, the resistance of point 27 on curve D is approximately 3 1O ohms.

Fig.5 shows a circuit in which a high resistor is generally used. An ionchamber 30 is indicated, havinga collector plate 31 and guardrings 32.The'collector plate is connected directly to a control electrode in anamplifier tube 33. Between the control electrode and the cathode circuit(ground) a high resistance unit'35 (10 ohms) is connected and thevoltage drop across this resistor is applied to the control electrodeto'control the anode current and produce a change of reading in'a meter34. A current of one micro-microampere through this resistor unit 35from collector 31 to ground will produce one volt change of potential onthe control'electrode and a corresponding change of current in meter 34;Voltagedivider 36 and battery 37 can be used to change the-sensitivityof the device as described above.

In the above description of the operation it has been assumed that theWireelectrodes were positive with respect to the cylindrical electrodeas indicated in the drawing. It should be pointed out herethat reversedpolarity can be applied with about the same results since an ionized gaswill conduct equally Well in either direction.

While there have been described and illustrated specific embodiments ofthe invention, it will be obvious that variouschanges and modificationscan be made therein without departing from the field of the inventionwhich should be limited onlyby the scope of the appended claims.

I claim:

1. A variable high resistor comprising, an envelope containing ionizablegas, three electrodes within the envelope, each electrode having alead-in conductor for external connection, a quantity of radioactivematerial within the envelope which produces gas ionization, and meansfor applying a variable voltage across a first and second of said threeelectrodes to deionize a portion of the ionized gas, said variablevoltage controlling the resistance between the first and third of saidthree electrodes and also controlling the range of the linear resistancecharacteristic between said first and third electrodes.

2. A variable high resistor in accordance with claim 1 wherein saidvariable voltage has a maximum value which is less than the ionizingpotential of the gas.

3. A variable high resistor in accordance with claim 2 wherein thesecond and third of said electrodes are symmetrically positioned withrespect to the first electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,457,973 Blau Jan. 4, 1949 2,497,213 Downing Feb. 14, 1950 2,616,986Coleman Nov. 4, 1952 2,629,837 Benade et al Feb. 24, 1953 2,657,316Friedman Oct. 27, 1953 FOREIGN PATENTS 776,272 France Oct. 31, 1934

